Conventionally, an inkjet recording device has been known as an image forming apparatus such as a printer, a facsimile machine, a copier, and a multifunctional peripheral having those functions, the image forming apparatus employing the liquid-ejection recording method in which, for example, a recording head ejecting ink droplets is used. The image forming apparatus employing the liquid-ejection recording method is capable of ejecting droplets from its recording head onto a fed sheet (or an OHP sheet or any medium on which ink droplets or other liquid can be applied, and may be referred to as a recording medium, a recording paper, a recording sheet, or the like) to form (the terms “form”, “record”, “type”, “image”, and “print” may be regarded as synonymous with each other) an image on the fed sheet. The image forming apparatuses employing the liquid-ejection recording method include a serial-type image forming apparatus in which its recording head moves in the main scanning direction and ejects droplets to form an image, and a line-type image forming apparatus in which its recording head ejects droplets to form an image without moving.
In this description, the term “image forming apparatus” employing the liquid ejection recording method refers to an apparatus capable of forming an image by ejecting a fluid onto a medium such as a piece of paper, strings, fibers, silk fabric, metal, plastics, glass, wood, and ceramics. Further, the term “image forming” refers not only to forming an image having significant information such as letters or figures onto a medium but also to forming an image having no significant meaning such as patterns onto a medium (including a case where ink droplets are just discharged onto a medium). Further, the term “ink” is not limited to a material generally called ink but refers to any material which becomes a fluid upon being ejected such as DNA samples, resists, and pattern materials.
In such an image forming apparatus employing the liquid ejection recording method, ink droplets are formed out of ink including coloring material. Because of this feature, such image forming apparatus may have a drawback causing problems such as the feathering in which dots formed by droplets have an irregular (beard) shape, and color bleeding in which when ink droplets having different colors are applied adjacent to each other on a sheet, the ink droplets having different colors are mixed on the boundary between the droplets, thereby blurring the color on the boundary. In addition, there is another problem that it takes time to dry the droplets after being applied to the sheet.
To overcome the problems, according to, for example, Patent Document 1, a heating unit is provided for heating before or after the printing to control ink bleeding and dry the ink droplets quickly after being applied to the sheet. According to Patent Document 2, a pretreatment fluid is applied to the sheet by using an application roller so that the pretreatment fluid reacts with the ink droplets to control ink bleeding. According to Patent Document 3, a pretreatment fluid is ejected in a mist form from a fluid ejection head, and according to Patent Document 4, a treatment fluid is applied before or after printing to improve ink fixing performance.
[Patent Document 1] Japanese Laid-Open Patent Application No. H8-323977
[Patent Document 2] Japanese Laid-Open Patent Application No. 2002-137378
[Patent Document 3] Japanese Laid-Open Patent Application No. 2005-138502
[Patent Document 4] Japanese Laid-Open Patent Application No. 2003-205673